Right now I’m creating a nightly restic snapshot of my server on borgbase and on some spare drives, and keeping the snapshots forever. There’s a ton of daily churn in my data though, between databases and logs and other files that don’t constitute ‘real data’ but might be needed to restore the app.
I guess OPs question is more about what makes you comfortable.
Is your drive only big enough for 2 backups or is it big enough for hundreds? If it was half that size would you still be happy with the number of backups? A quarter of the size?